The present invention relates generally to a speaker applicable to an automotive audio system capable of producing high-quality audio sound, especially relatively low-frequency sound. More specifically, the invention relates to a vehicle panel speaker which can be driven at high amplitudes without requiring excessively high driving power.
Generally, speakers for automotive audio systems can be installed at various locations in the vehicle compartment. Conventionally, cone-type speakers are used in automotive audio systems to reproduce audio sound over a suitable frequency range. However, since space in the vehicle compartment available for the speakers is seriously limited, the size of cone-type speakers to be installed in the vehicle compartment must be limited. On the other hand, in order to clearly reproduce relatively low-frequency sounds, such speakers must be relatively large. For example, at a frequency of 500 Hz, the speaker diameter must be approximately 20 cm. Such a large diameter speaker cannot be installed in the vehicle compartment without significantly reducing the free space in the vehicle compartment. Particularly, in an audio system having recessed speakers disposed between inner and outer vehicle panels or installed below the rear parcel shelf, the size of the speaker which can be used is strictly limited.
Consequently, for standard passenger cars, speakers with a diameter of 5 to 10 cm are generally used. This degrades the audio sound reproduction quality, particularly with respect to relatively low-frequency sound.
In view of the above, there has been proposed a speaker utilizing a vehicle panel as a sound-producing or amplifying medium. Such a speaker comprises a vehicle panel and a driver unit associated with the vehicle panel, at least a part of which is adapted to oscillate to produce audio sound when driven by the driver unit.
The present invention is generally an improvement of the foregoing prior invention for obtaining better quality and higher amplitude audio sound reproduction.